It is well known that siloxane homo- and copolymers can be prepared to provide an advantageous balance of properties and economics. Moreover, in comparison with mixtures of homopolymers, copolymers are generally more effective in producing any desired property, and the tendency to separate on a microscopic scale is avoided. Homopolymers can be made by polymerizing the cyclic siloxanes, subject to the difficulties mentioned hereinafter, if one of the silicon-bonded substituents comprises an aliphatic radical or haloaliphatic radical of 3 carbon atoms or greater. Copolymers of diorganopolysiloxanes can also be prepared by mixing and polymerizing the respective cyclic siloxanes, but, again, if one of them has a silicon-bonded aliphatic or haloaliphatic radical of three carbon atoms or greater, then only up to 20 mol % of the other co-monomer, which does not include such a structural limitation, can be incorporated. Johannson, U.S. Pat. No. 3,002,951, illustrates the problem and the limitation. Johannson discloses that if a cyclic trisiloxane, having a 3 or more carbon silicon-bonded organo substituent, is reacted in admixture with another cyclic diorganosiloxane compound, in the presence of a strong alkali catalyst, under non-equilibrating conditions, only up to 10 mol % of the co-monomer will polymerize. It is stated in Johannson that if one starts with cyclic tetrasiloxanes and subjects them to the same alkaline polymerization conditions, that no apparent polymerization occurs. At the other end of the composition range, Polmanteer et al., U.S. Pat. No. 3,050,492 disclose that only up to about 15 mol % of fluorosilicone can be copolymerized under equilibration conditions.
Surprisingly, now, it has been discovered that potassium hydroxide, alone, or as the silanolate, can be complexed with cyclic polyethers (the so-called Crown ethers) and the complex is very efficient to catalyze homo- and copolymerization of a very wide variety of cyclics, including the difficult or previously thought to be impossible ones, into oils and gums of substantial commercial utility. Moreover, copolymerization of the cyclic tetramer with other cyclic co-monomers will occur over a wide variety of composition ranges, and is not limited to the 90 mol % maximum found under non-equilibrating conditions with the cyclic trimer as reported by Johannson, or the 15 mol % maximum found under equilibrating conditions by Polmanteer et al.
The process using the new catalysts of this invention has many important advantages. It permits the use of cyclic tetramers which are more readily obtained from hydrolyzate cracking than the trimers used by Johannson (although the latter can be used). Tetramers substituted with "difficult" substituents, readily homo- and copolymerize. The process can be employed with conventional chain-stoppers to provide homo- and copolymers with molecular weights varying over a wide range, to produce oils and gums. Polymerization is generally rapid. Conversion of the cyclic starting materials to the desired polymerized products are generally high. Residues of catalyst are readily removed and any residue from the cyclic polyether catalyst component does not adversely affect, e.g., destabilize, the resultant polymer or copolymer.
The present invention is of prime importance in the use of methyl-3,3,3-trifluoromethylsiloxane cyclic tetramer as a starting material. Both Johannson, cited above, and Pierce et al., U.S. Pat. No. 2,979,519, disclose that such cyclic tetrasiloxanes cannot be homopolymerized. Moreover, the catalyst and conditions set forth herein permit the copolymerization of this fluorosilicone tetramer with dimethyl tetramer (or dimethyl trimer) in the range of 30 to 98 mol % fluorosilicone. The ability to produce such copolymers is an advance in the art since, if the full solvent resistance properties of the fluorosilicone were not needed, a blend of fluorosilicone polymer with methyl polymers would be necessary. However, a copolymer is more efficient in solvent resistance than a blend at the same fluorosilicone content. In addition, while stable blends of fluorosilicone and methyl polymers can be made for high viscosity gums, it is impossible to make stable blends of lower viscosity oils, such as would be used in room temperature vulcanizing and fluid products, because the incompatibility of the fluorosilicone oil with the methyl oil will cause separation of these two components. Thus, the best balance of economy and solvent resistance is achieved.
It is, accordingly, a principal object of the present invention to provide a process for producing diorganopolysiloxane homo- or copolymer gums or oils in high yield, using a cyclic monomer, and especially those wherein at least one of the organo groups attached to the silicon atom is aliphatic or haloaliphatic of at least three carbon atoms or more.
Another object of the present invention is to provide low molecular weight diorganopolysiloxane homo- and copolymer oils and gums having a viscosity from 30 to 200,000,000 centipoise at 25.degree. C. and particularly those wherein at least one of the organo groups attached to the silicon atoms in one of the co-monomers is aliphatic or haloaliphatic of 3 carbon atoms or more, by a process comprising equilibrating cyclic siloxanes, alone, or in admixture of cyclic co-monomers in the presence of certain novel crown ether-cation-complex catalysts.
A further object of the present invention is to provide diorganopolysiloxane copolymer oils or gums having a viscosity from 30 to 200,000,000 centipoise at 25.degree. C., wherein at least one of the co-monomers comprises 30 to 85 mol % of the copolymer units, and includes organo groups attached to the silicon atoms having at least 3 carbon atoms, and particularly, a --CH.sub.2 CH.sub.2 R.sup.7 substituent group, where R.sup.7 is perfluoroalkyl, using a cyclic tetrasiloxane as a co-monomer.